Not applicable.
Not applicable.
The present invention relates generally to analog integrated circuits and more specifically to providing feedback from a high-voltage output to a control circuit.
In electronic systems, such as a telecommunications or computer system, it is often desirable to add or remove one or more electronic components from the system. For example, a user may desire to disconnect a printer or external disk drive from a computer system, or to add or remove a telephone expansion card from a telephone system. Many systems require or suggest that the system be turned off before adding, removing, or swapping components; however, this means that the system will have to re-start, typically consuming time that could otherwise be spent more productively.
It is generally more desirable to xe2x80x9chot swapxe2x80x9d components, in other words, to change a component while the system is powered. Some components operate at relatively low voltage, i.e. less than about xc2x112 V, and have a sufficiently high input impedance on the power line to the component that there is relatively little draw on the system power supply when the component in plugged into the system. These components can usually be added or removed with the power on, as long as such handling does not damage the component.
Other components need additional circuitry to allow hot swapping. In particular, many electronic devices operate at relatively high voltages, i.e. about 36 to 100 V and xe2x88x9236 to xe2x88x92100 V, or power is distributed to components at a high voltage, and stepped down to the desired operating voltage. Hot swapping some of these devices can cause an in-rush of current that pulls the system power supply voltage down, adversely affecting and perhaps damaging other system components. The inrushing current can also damage the component that is being plugged in. Some devices use a relatively large bypass capacitor, typically hundreds of microfarads, between the high-voltage input and ground, which causes a large inrushing current when the component is plugged in and the capacitor is quickly charged to the supply voltage (according to I=Cdv/dt). One way to limit the inrushing current and hence maintain acceptable system voltage levels is to control the rate at which the supply voltage changes on the swapped device.
A high-voltage field-effect transistor (xe2x80x9cFETxe2x80x9d) is one type of device that can be used as a variable electronic switch to control the current delivered to the load, although other suitable devices are known in the art. A control signal (voltage) applied to the gate of the FET controls the current flowing between the drain and the source of the FET. In one type of control circuit, a capacitor connecting the output (drain) of the FET with the FET gate can limit the rate of change of voltage at the output of the FET by providing negative feedback. This type of feedback is often referred to as Miller feedback or Miller compensation, and the associated capacitor is known as a Miller capacitor. Although Miller feedback is often used in amplifier systems to move unwanted poles outside of the frequency operating range of the amplifier system, in this instance the Miller capacitor is used to control the slew rate of the output voltage from the power supply when a component is hot-swapped.
However, with high-voltage power supplies a high-voltage capacitor is needed in the feedback loop. Otherwise the capacitor would almost certainly fail due to dielectric breakdown. Thus, Miller capacitors used for controlling the slew rate of high-voltage output ports are external capacitors that are assembled onto a circuit board along with other control components, such as the gate current driver. It is generally desirable to limit the number of discrete, external components because they add component cost, assembly cost, and the connections (e.g. solder joints) provide additional potential failure points.
Therefore, it is desirable to provide a high-voltage output circuit with a controlled slew rate allowing hot-swapping of electronic components at the output port without using a high-voltage external capacitor.
An integrated Miller feedback circuit is used to control the in-rush current of an expansion board during hot-swapping and similar applications. The integrated circuit dispenses with the need for an external high-voltage, high-capacitance capacitor by attenuating a high-voltage output signal taken from the output node of an electronic semiconductor switching device. The attenuated feedback voltage is provided to one terminal of an integrated thin-film capacitor. The other terminal of the integrated thin-film capacitor is connected to a high-impedance internal feedback node. An integrated current source with a high output impedance provides or sinks current from the internal feedback node. An integrated voltage buffer amplifier between the internal feedback node and the control node of the electronic semiconductor switching device, e.g. the gate of a power FET, provides the control signal output.